In various compressors systems, as, for example, compressors utilized in vapor compression refrigeration systems, oil is typically used for lubrication of moving parts within the compressor. Not untypically, the lubricating oil and the refrigerant that is to be compressed by the compressor have a relatively high affinity for each other in the sense that the refrigerant readily goes into solution within the oil. As these compressors include a sump into which the lubricating oil is drained, and such sump is commonly in fluid communication with the compressed refrigerant side of the compressor, the sump will contain a mixture of refrigerant and oil which may approach a one to one ratio.
As with the case of most solutions of gases within liquids, the colder the lubricant, the greater the solubility of the refrigerant therein. As a result, solubility of refrigerant in the lubricating oil will typically be the greatest when the system has been dormant for a while, that is, has not been operating such that the lubricant will have been warmed as it lubricates and cools relatively moving parts of the compressor.
In certain applications, such as aerospace applications, vapor compression refrigeration systems are utilized to cool electronic components. It is not unusual for such systems to be exposed to ambient temperature in the neighborhood of -40.degree. F. with the consequence that if the system shuts down because of low demand for refrigeration, it will quickly cool and a great deal of refrigerant will be in solution within the lubricant when compressor operation is again called for.
This in turn causes two difficulties in the system. Firstly, because the lubricating oil is diluted by the large amount of refrigerant in solution, lubricity is lowered which in turn means increased wear rates for such time as the lubricity is low. Secondly, with the refrigerant in solution, it is not effectively in the vapor compression circuit which means that the efficiency of operation of the vapor compression circuit is decreased for so long as the refrigerant remains in solution. That is to say, there will be a lag in achieving full cooling capability in the operation of the vapor compression system until the refrigerant is driven out of solution in the lubricant.
The present invention is directed to overcoming one or more of the above problems.